1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery.
2. Description of the Related Art
Lithium ion secondary batteries and other nonaqueous electrolyte secondary batteries are increasingly important as vehicular power sources or as power sources for, e.g., personal computers and mobile devices. In particular, lithium ion secondary batteries, which are lightweight and provide high energy densities, are preferred for use as high-output vehicular power sources. A typical configuration of this type of nonaqueous electrolyte secondary battery is provided with an electrode assembly in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, the positive electrode having a structure in which a positive electrode active material layer containing a positive electrode active material is supported on a positive electrode current collector, and the negative electrode having a structure in which a negative electrode active material layer containing a negative electrode active material is supported on a negative electrode current collector. The following, for example, are used as the positive electrode active material: layer-structured lithium cobalt composite oxides (for example, LiCoO2), layer-structured lithium nickel composite oxides (for example, LiNiO2), spinel-structured lithium manganese composite oxides (for example, LiMn2O4), and spinel-structured nickel-containing lithium manganese composite oxides (for example, LiMn1.5Ni0.5O4). Japanese Patent Application Laid-open No. 2014-103098 indicates that an inorganic phosphate compound that contains an alkali metal and/or alkaline-earth metal (for example, Li3PO4) is added to a positive electrode active material layer in a nonaqueous electrolyte secondary battery containing a positive electrode active material. According to Japanese Patent Application Laid-open No. 2014-103098, the elution of metal from the positive electrode active material can be reduced and the battery durability (for example, the capacity retention ratio) can be enhanced by the addition of this inorganic phosphate compound to the positive electrode active material layer.